This invention relates to a power failure protected power supply device and, especially, to an improved power failure protected power supply device of voltage boosting type.
FIG. 1 shows a typical example of the power failure protected power supply device of this type according to the prior art, whose principle is disclosed, for example, in the Japanese opened utility model gazette No. H5(93)-25953. As shown, the device includes a pair of input terminals 10 and 12 to be connected to a commercial a.c. power supply of 100 volts, for example, and the input terminals 10 and 12 are connected through a high frequency noise removing coil 14 and a current limiting resistor 16 across a capacitor 18. The current limiting resistor 16 is connected in parallel with a triac 20. A full-wave charging circuit including switching elements 24 and 26 and capacitors 28 and 30 is further connected through an input reactor 22 across the capacitor 18 and the switching elements 24 and 26 are connected respectively in inverse parallel with diodes 32 and 34. The switching elements 24 and 26 may be insulated gate bipolar transistors (hereinunder referred to as IGBTs), for example.
During a positive halfwave period having a potential at the input terminal 10 which is higher than that at the input terminal 12, an input current flows through the high frequency noise removing coil 14 and current limiting resistor 16 to charge the capacitor 18. The voltage across the capacitor 18 becomes 140 volts when the effective value of the input voltage is 100 volts. Upon completion of charging, the triac 20 receives a gating signal from its control circuit (not shown) and comes into conduction to short-circuit the current limiting resistor 16. Throughout this period, the switching element 24 receives a gating signal at a frequency of 15 to 20 kilohertz, for example, from its control circuit (not shown) to repeat an ON-OFF operation. When the switching element 24 is in ON state, the input current through the triac 20 flows through the reactor 22 and the switching element 24 to the capacitor 28 together with the charge in the capacitor 18 to charge the same. At this time an energy is stored in the reactor 22. When the switching element 24 comes in OFF state, an inverse electromotive force is induced across the reactor 22 in the arrow direction by the stored energy and a sum of the inverse electromotive force and the voltage across the capacitor 18 is applied through the diode 34 to the capacitor 30. Thus, the capacitor 30 is charged in a polarity as shown and its voltage rises up to 280 volts, for example, while it is rendered 200 volts by control of the switching element 24.
On the other hand, during a negative halfwave period having the potential at the input terminal 10 lower than that at the input terminal 12, the input current flows from the input terminal 12 through the high frequency noise removing coil 14, capacitor 18, triac 20 and coil 14 to the input terminal 10 to charge the capacitor 18 in the opposite direction to the above. The input current also flows from the input terminal 12 through the high frequency noise removing coil 14, capacitor 28, diode 32, reactor 22, triac 20 and coil 14 to the input terminal 10 to charge the capacitor 28 in a polarity as shown. The switching element 26 also receives a gating signal at a frequency of 15 to 20 kilohertz, for example, from its control circuit (not shown) to repeat an ON-OFF operation throughout this negative half-wave period. When it is in the ON state, the current from the input terminal 12 through the high frequency noise removing coil 14 flows through the capacitor 30, switching element 26, reactor 22, triac 20 and coil 14 to the input terminal 10 together with the charge of the capacitor 18 to charge the capacitor 30 in the opposite polarity to what is shown. At this time, an energy is stored in the reactor 22. In the OFF state of the switching element 26, an inverse electromotive force is induced in the reactor 22 in the opposite direction to the arrow direction by the stored energy and a sum of the inverse electromotive force and the voltage of the capacitor 18 is applied through the diode 32 to the capacitor 28. Thus, the capacitor 28 is charged in the polarity as shown and its maximum voltage becomes about 200 volts under control of the switching element 26 as same as the above.
Thus, a boosted voltage is generated across the capacitors 28 and 30. Switching elements 36 and 38 constituting an invertor are further connected across the series connection of capacitors 28 and 30 and the junction between the switching elements 36 and 38 is connected through an output reactor 40 and a high frequency noise removing coil 42 to output terminals 44 and 46. The switching elements 36 and 38 may also be IGBTs and have diodes 48 and 50 respectively connected thereto in inverse parallel fashion.
During the above-mentioned positive halfwave period of the input a.c. voltage, if one switching element 38 is put into conduction for a predetermined time by a gating signal from its control circuit (not shown), the charge in the capacitor 30 flows through the switching element 38, output reactor 40, high frequency noise removing coil 42, output terminal 44, external load (not shown), output terminal 46 and coil 42. If the other switching element 36 is put into conduction for the predetermined time by a gating signal from its control circuit (not shown) during the negative halfwave period, the charge in the capacitor 28 flows through the high frequency noise removing coil 42, output terminal 46, external load (not shown), coil 42, output reactor 40 and switching element 36. In other words, an a.c. voltage synchronized with the input a.c. voltage is applied to the external load. The value of this output a.c. voltage is determined by the above-mentioned conduction time of the switching elements.
A switching element 52 such as bipolar transistor and a storage battery 54 are further connected in series across the series connection of the capacitors 28 and 30 and a diode 56 is connected to the switching element 52 in inverse parallel fashion. The switching element 52 is put into conduction by a gating signal from its control circuit (not shown) to charge the battery 54 with the charges of the capacitors 28 and 30. Even if the input a.c. voltage stops, the voltage across the battery 54 is converted into an a.c. voltage as same as the above and applied to the external load so long as the control circuit of the invertor means operates continuously to put the switching elements 36 and 38 into conduction alternatingly.
Numeral 58 denotes a triac connected between the input and output of the power supply device. When it is put into conduction by a gating signal from its control circuit (not shown), the input terminal voltage is applied through the high frequency noise removing coils 14 and 42 to the output terminals. Accordingly, it is possible to execute maintenance and inspecting operations for the power supply device in this state.
As described above, the voltages across the capacitors 28 and 30 become about 200 volts respectively when the commercial input voltage is 100 volts in this power supply device. Accordingly, the storage battery 54 to be substituted therefor at the time of power failure must be one which can generate a voltage above 400 volts and it involves such a problem of increased capacity of the battery 54 and accompanying increased size and weight of the device as a whole.
Accordingly, an object of this invention is to provide an improved voltage boosting power failure protected power supply device which can generate a high voltage using a battery of small capacity.